Berryhill and Merriwether, 20-something sisters, are first off the ship, bounding onto the ice ledge — pronounced sturdy and safe by our watchful naturalists — for a gasp of solitary grandeur. For one precious moment, the three of us are the only people on this silent, icy planet.

It will be a few minutes, still, before our shipmates will haul on parkas and join us on the shelf where our captain has moored our ice-hardened ship, literally crunching into the crust so we can walk from gangplank along the crusty sheet.

For now, we are Scott and Amundsen and Shackleton combined, explorers in a vast untouched universe — though in far more comfortable circumstances, with fluffy duvets, schnapps-laced hot chocolate and home-baked cheesecake plated on a chocolate crunch.

Our voyage aboard the 148-passenger National Geographic Explorer comes 100 years after Sir Ernest Shackleton’s final, treacherous expedition, and 50 years after Lindblad Expeditions, which runs the National Geographic sailings, first brought tourists to Antarctica.

During our nine-night December sailing from Argentina, a total of 15 vessels will bring visitors through the Southern Ocean and along the Antarctic Peninsula. We will see only one — a surprisingly small sailboat of intrepid travelers — as we steam through the Gerlache Strait on the west side of the Antarctic Peninsula, then slip east into the Weddell Sea on our 2,000-mile voyage.

OUR VOYAGE COMES 100 YEARS AFTER SIR ERNEST SHACKLETON’S FINAL EXPEDITION, AND 50 YEARS AFTER LINDBLAD EXPEDITIONS, WHICH RUNS THE NATIONAL GEOGRAPHIC SAILINGS, FIRST BROUGHT TOURISTS TO ANTARCTICA.

We have expedition leader Lisa Kelley — on her 121st Antarctic foray — and careful coordination between visiting vessels to thank for our solitude. When it comes to tourism, Antarctica is one of the most closely regulated regions on the planet, thanks to the environmental commitment of the 25-year-old International Association of Antarctica Tour Operators, which works with the governing Antarctic Treaty organization.

But first, the dreaded Drake Passage.

One hundred million years ago or so, Antarctica was connected to Australia and South America. Today 600 miles of open water lie between Tiera del Fuego and Antarctica, a stretch notorious for its furious winds, swaggering waves and unpredictability. The 36-hour journey can be as placid as a bathtub or uproarious enough to send a stalwart to the porcelain bowl.

Our crossing rates a 6 out of 10, we’re told, with 15-foot swells and winds that can drop a six-foot man. Snug inside, we stagger through corridors grasping handrails and the stout ropes that have been tied across open lounges. The skies are variable: one minute hailing, the next sunny, the next so foggy the waves outside the window disappear altogether. Then it’s back to snow and sun again.

“It’s the price we pay,” says Capt. Oliver Kruss, “to get to this magnificent environment.”

For most passengers, a scapolomine patch and Dramamine do the trick — though it’s wise to keep one hand clutched around your café au lait.

“It’s like having a hangover without the party the night before,” says Steve Weissman of Aventura. “The only thing funnier than watching other people move is trying to move yourself.”

That explains why we spend much of the crossing reading in the library or in the cushioned chairs of the ship’s main lounge. The day is spent preparing: meeting the expedition team members — geologist; natural historian; experts in birds, whales and sea ice, all certified as photo instructors; watching presentations on currents and local seabirds. Most of our fellow travelers are widely traveled — given the cost and rigor, Antarctica falls deep into the bucket list — and retired, with a few adult children and parents in the mix.